Conventionally, for the purposes of improving fuel efficiency of an automobile, reducing an environmental load, and the like, an automatic idle-stop system, which automatically performs idle-stop when a predetermined condition is satisfied, has been developed. For example, with regard to a method for bringing a starter pinion into meshing engagement with a ring gear and a starter controller, there exists an engine starting device, in which, when an rpm of the ring gear is within a predetermined range and a direction of rotation is forward, the pinion gear is brought into meshing engagement with the ring gear, thereby realizing meshing state between the pinion gear and the ring gear in an early stage (see Patent Literature 1).
There also exists an engine starting device for predicting an engine rpm NE after elapse of predetermined time T(s) and determining a super-low rotation state to perform a normal restart when NE is smaller than a controllable minimum rpm Nemin of a pinion gear (see Patent Literature 2).